11. The way to cure juvenile diabetes

Big business
In 2016, the estimated number of people suffering from diabetes mellitus worldwide is 422 million (3). The proportion of juvenile diabetics is estimated at 5% (2) to 10% (3). Thus between 20 and 40 million humans suffer from T1D, their lives depending on daily insulin injections. And their number is growing with increasing speed. The only option is to administer insulin, there is no cure for juvenile diabetes. The research into such a cure is big business. For example, in 2007 the pharmaceutical company Eli Lilly licensed teplizumab as a promising drug for curing juvenile diabetes, with a $ 41 million up front and a billion dollars pledged for milestones (16). A real T1D cure will phase out daily insulin injections. Which will be a landslide, both in the pharmaceutical field as well as in health care.

Gene therapy
The origin of juvenile diabetes is in the DNA. Its hereditary predisposition varies up to a maximum of 19 deviating gene variants. Thus to tackle this disorder at its source, gene therapy seems indicated (10). However, recent corrections made in the genetic makeup of embryo’s by Chinese researchers, did not improve ‘bad genes’, while disturbing a lot of ‘good genes’(1). So gene therapy, as a cure for T1D, seems not to be for the near future.

Stopping the auto-immune reaction
Another intervention to cure juvenile diabetes might be in stopping the auto-immune reaction in the pancreatic islets. Nowadays, most auto-immune diseases are treated by a nearly general suppression of the immune system, for example by prednisone or ciclosporin. However, that effect is only temporary so that lifelong medication is necessary. Those drugs have serious toxic side effects, while general immune depression involves a risk of various infections. Therefore, the selective shutdown of derailed immune cells is preferable. To that end, monoclonal antibodies are in use. They shut down certain immune cells by targeting specific receptors on their cell membrane. But they do not destroy these cells. So the beneficial effect of monoclonal antibodies is also temporary, and again lifelong medication is needed. Most of these monoclonal antibodies also have severe side effects. Thus the advantage of selective compared to general immune suppression is only in the smaller risk of secondary infections.

CD8 monoclonal antibody
In juvenile diabetes, the selective shutdown of islet autoreactive CD8 T cells requires a monoclonal antibody that targets CD8 receptors on the membrane of those T cells. Monoclonal antibodies are produced by cloning specific 'parent cells' in transgenic mice or by phage display (12). As these are living organisms, the resulting monoclonal antibodies are called ‘biologicals’. However, available CD8 biologicals are neutralizing all CD8 T cells, not only the islet autoreactive CD8 T lymphocytes. Moreover, those commercially available CD8 biologicals are only licensed for diagnostic laboratory tests (4). Therapeutic use in type 1 diabetic patients needs a fully human biological that specifically targets the islet autoreactive CD8 T cells, leaving normal CD8 T cells alone. ‘Fully human’ means that the biological has been derived from a human parent cell. Thus it does not invoke an immune response against foreign proteins in humans (12). In the case of juvenile diabetes, that parent cell to be cloned for antibody production must be an islet autoreactive CD8 T lymphocyte. Which can be found in the inflamed pancreatic islets of T1D patients in post mortems. The monoclonal antibody against such CD8 T cells could be named oktolimumab. The prefix okto (eight) referring to the CD8 receptor to which the antibody affixes. And according to the nomenclature of monoclonal antibodies, lim indicates the targeted lymphocytes; the letter u is for the fully human nature of the antibody and mab stands for monoclonal antibody (14).

ADC
A recent technique to reduce the side effects of toxic drugs is by engineering an ADC (Antibody-Drug Conjugate) i.e. a monoclonal antibody conjugated to a chemotherapeutic (cytotoxic) drug (7). Nowadays, ADCs are engineered for cancer therapy. The monoclonal antibody specifically targets certain cancer cells, which subsequently are destroyed by the chemotherapeutic drug. By combining the unique targeting capabilities of a biological with the killing ability of a cytotoxic drug, an ADC allows discrimination between healthy and diseased tissue (8). Thanks to the selective release of the cytotoxic drug (only in the cancer cells), its dosage can be considerably lower and side effects are substantially diminished. Thus it is possible to use drugs 100 to 1000 times more cytotoxic for cancer cells than chemotherapeutics that are in use today (7).

Vedotin
A potent cytotoxic drug is vedotin. It is derived from a marine mollusc. After invading a cell, it splits off monomethyl auristatin E (MMAE), which inhibits cell division and causes cell death (13). Because of its toxicity, MMAE cannot be used as a drug by itself. But when conjugated (as vedotin) to a monoclonal antibody, it selectively kills the target cells, meanwhile avoiding most of its toxic side effects. Therefore, the link between the biological and vedotin must be stable, so that it is not cleaved before it has entered the targeted cancer cells.

ADC and cancer
Anno 2017, only two ADCs have been approved for cancer therapy so far:
- Brentuximab-vedotin (Adcetris®) is in clinical use for Hodgkin lymphoma (HL) (9). The monoclonal antibody brentuximab targets the cell-membrane receptor CD30 of the cancer cells. Inside these cells, the ADC splits off MMAE which kills the cells.
- Trastuzumab-emtansine (Kadcyla®) is approved for HER2-positive breast cancer (17). The monclonal antibody trastuzumab targets the receptor HER2 in those breast cancer cells. The cytotoxic agent emtansine subsequently destroys the cells.

ADC and juvenile diabetes
In juvenile diabetes, islet autoreactive CD8 T cells can be considered cancer cells. So an ADC that selectively kills these cells requires a monoclonal antibody that specifically targets this type of lymphocytes. Such a biological is (or hopefully will be soon) oktolimumab. The conjugated cytotoxic drug could be vedotin. This newly to be engineered ADC oktolimumab-vedotin must target and destroy islet autoreactive CD8 T cells, leaving the rest of the immune system intact. As a result, the auto-immune reaction in the pancreatic islets will stop, enabling recovery of residual β cells and the restart of insulin production. In patients with insufficient revival of β cells, implantation of stem cells (as extra β cells) might complete the cure for juvenile diabetes.

Control of the cure
After destruction of all islet autoreactive CD8 T cells by (ev. repeated doses of) oktolimumab-vedotin, the residual β cells will regain control of the blood glucose concentration and will restart insulin production, thus gradually banning the daily insulin injections. Outcome measures for this ADC therapy will be two blood tests:
1. anti-GAD: decrease of the antibodies against GAD reflects the release of the auto-immune reaction in the pancreas of type 1 diabetics.
2. C-peptide: recovery of the C-peptide concentration reflects the restart of the patient’s own insulin production.

Relapse
Both laboratory tests mentioned above also monitor a possible relapse to type 1 diabetes after a foregoing cure. Even a complete cure for juvenile diabetes will not necessarily be permanent, because the aberrant gene-variants in the DNA continue to code for faulty maturing of CD8 T cells in the thymus. However, from puberty onwards, the thymus is shrinking. Thus the older the T1D patient is at the time of a successful intervention therapy, the less active the thymus will then be in producing autoreactive CD8 T cells and the smaller the chance of a relapse of juvenile diabetes.

Dogs
The approval of oktolimumab-vedotin as a new therapeutic drug in juvenile diabetes, is a big and promising challenge. Such a license requires a lot of research, involving laboratory animals as well as test subjects and T1D patients. To that end, spontaneous diabetic dogs might be helpful. So far they are beyond the scope of researchers in human diabetes. Diabetes mellitus is a common endocrinological disease in dogs (6). In more than half of spontaneously diabetic dogs, the disease resembles type 1 diabetes in humans (6). It is a hereditary predisposition found in certain dog breeds. Once the disorder is manifest, the dogs must be treated by daily insulin injections to survive. And antibodies against β-cells can be found in their blood. Thus a disturbance in the function of certain T lymphocytes in these dogs seems a realistic assumption (6).

Pilot study
The ADC oktolimumab-vedotin might be tested for its curing capacity in diabetic dogs. Because they will be of various breeds, their size and weight can considerably differ. Therefore the ADC should be dosed in mg/kg body weight. Subsequently, doses could be increased step-by-step in, for example, monthly intervals. That might yield preliminary insight into the curing capacity and the side effects of the ADC. If one or more dogs could be cured that way, it would give an enormous boost to the research into the cure for human juvenile diabetes.

Conclusions
1. Anno 2016, there were between 20 and 40 million humans with juvenile diabetes worldwide; so research into the cure for type 1 diabetes is big business.
2. Selective suppression of certain immune cells by monoclonal antibodies has a temporary effect and therefore it demands lifelong medication.
3. A fully human monoclonal antibody against islet autoreactive CD8 T cells (oktolimumab) will selectively target those derailed T cells.
4. The ADC oktolimumab-vedotin will selectively destroy islet autoreactive CD8 T cells, thus stopping the shutdown of β cells; as a result, residual β cells can restart insulin production.
5. For someone who is cured of juvenile diabetes, the risk of relapse diminishes with age, because the thymus starts shrinking from puberty onwards.
6. New drugs to cure juvenile diabetes might be tested in dogs suffering from spontaneous diabetes mellitus, because the disorder in many of those animals is similar to type 1 diabetes in humans.